Worldwide dependence on fossil reserves for the production of chemicals and fuels is alarming, as these resources are expected to exhaust gradually. Therefore, synthesis of renewable fuels from biomass has become an important area of research; to replace petroleum based fossil oils. Biomass has drawn much attention due to its potential to produce valuable organic compounds, chemicals and fuels. Hydrogenation/hydrogenolysis is an important process for the utilization of biomass, as biomass-derived materials have high oxygen content. 5-Hydroxymethylfurfural (HMF), which can be synthesized from hexoses, has been identified as a key player in the biobased renaissance, because it can be converted into levulinic acid, ethyl levulinate, γ-valerolactone, as well as the promising fuel 2,5-dimethylfuran (DMF). DMF is particularly attractive because of its superior energy density (30 kJcm−3), high research octane number (RON=119) and nearly ideal boiling point (92-94° C.). Furthermore it is immiscible with water and is easier to blend with gasoline than ethanol. Biomass derived DMF has been successfully tested as a biofuel in a single-cylinder gasoline direct-injection (GDI) research engine. The performance of DMF was satisfactory against gasoline in terms of ignition, emission and combustion characteristics. These attributes bode well for the use of DMF as an alternative liquid fuel for transportation.
There are several recent reports in the literature on the conversion of biomass to DMF. Dumesic and co-workers utilized a two-step process to convert fructose to DMF. The first step involved the dehydration of fructose to 5-hydroxymethylfurfural (HMF) by HCl in biphasic solvent conditions followed by vapor phase hydrogenation and hydrogenolysis of HMF with a Cu—Ru/C catalyst to form DMF. Thananatthanachon and Rauchfuss provided a milder pathway for the production of DMF using formic acid as a reagent and Pd/C as catalyst. The formic acid functioned as a hydrogen donor in second step and assists the deoxygenation of HMF to DMF. For the high yield of DMF, formic acid and H2SO4 must be used. Formic acid and H2SO4 are highly corrosive and are highly harmful to humans and environment, making this process less eco-friendly. Chidambaram and Bell presented catalytic conversion of HMF to DMF with a Pd/C catalyst in ionic liquids, which gave 15% DMF yield and 47% conversion of HMF. However, a potential drawback of this method was that the solubility of hydrogen in ionic liquids is low. Hence, a high pressure of H2 (62 bar) was required, which made the process energy intensive. Under similar reaction conditions, the Ru/C catalyst failed to produce DMF from HMF. Hansen et al. reported catalytic transfer hydrogenation (CTH) of HMF over Cu-containing mixed metal oxides using supercritical methanol and yielded 48% DMF. Gallo et al. studied the hydrogenolysis of HMF in the presence of lactones using a RuSn/C catalyst with a DMF yield up to 46%. Yang and Sen reported the conversion of biomass-derived carbohydrates to another promising liquid fuel 2,5-dimethyltetrahydrofuran (DMTHF) with good yield using homogeneous RhCl3 and RuCl3 catalysts. The same authors have also reported the synthesis of 5-methylfurfural (MF) from fructose by using heterogeneous Pd/C catalyst. Morikawa et al. studied the CTH of HMF using AlCl3 and Pd/C catalysts with a DMF yield up to 60%. These CTH routes have, however, several disadvantages, as they require the use of homogeneous acid co-catalyst to enhance the hydrogenation activity and these catalysts are difficult to separate from the reaction mixture.
U.S. Pat. No. 3,963,788 discloses a process for the conversion of carbohydrates to polyhydric alcohols. Carbohydrates, such as corn starch hydrolyzate, glucose, and invert sugar, are converted to polyhydric alcohols by hydrogenation at high pressure in the presence of a ruthenium-containing alumino-silicate zeolite catalyst in which the silica/alumina mol ratio is greater than three, and in particular ruthenium on a Y type zeolite in the hydrogen form.
US20080033188 discloses a catalytic process for converting sugars to furan derivatives (e.g. 5-hydroxymethylfurfural, furfural, dimethylfuran, etc.) using a biphasic reactor containing a reactive aqueous phase and an organic extracting phase wherein the aqueous reaction solution, the organic extraction solution, or both the aqueous reaction solution and the organic extraction solution contain at least one modifier to improve selectivity of the process to yield furan derivative compound. The catalyst contains very high Ru content (10 wt %), as a part of Cu—Ru [in 3:2 ratio] catalyst supported on carbon for the hydrogenolysis of HMF to DMF. The process also requires longer reaction time (10 h) to achieve good yield of DMF (79%).
US20100317901 discloses a catalyst composition which can include: a support; a ruthenium catalyst (Ru) nanoparticle; and a linker linking the Ru nanoparticle to the support, wherein the linker is stable under hydrogenolysis conditions. The linker can include 3-aminopropyl trimethoxysilane (APTS) or derivatives thereof or such as those with amine functionality or phosphotungstic acid (PTA) or other similar solid acid agents. The support can be selected from alumina, carbon, silica, a zeolite, TiO2, ZrO2, or another suitable material. A specific example of a support includes zeolite, such as a NaY zeolite. The Ru nanoparticle can have a size range from about 1 nm to about 25 nm, and can be obtained by reduction of Ru salts. The novel Ru catalyst can be used for hydrogenolysis of various polyols (e.g., higher polyols) to alcohols or lower alcohols with external hydrogen being added.
Article titled “The selective hydrogenation of biomass-derived 5-hydroxymethylfurfural using heterogeneous catalysts” by R Alamillo et al. Green Chem., 2012, 14, 1413-1419 reports the products produced by hydrogenation of biomass-derived 5-hydroxymethylfurfural (HMF) as potential sustainable substitutes for petroleum-based building blocks used in the production of chemicals. The hydrogenation of HMF over supported Ru, Pd, and Pt catalysts in monophasic and biphasic reactor systems is disclosed to determine the effects of the metal, support, solution phase acidity, and the solvent to elucidate the factors that determine the selectivity for hydrogenation of HMF to its fully hydrogenated form of 2,5-di-hydroxy-methyl-tetrahydrofuran (DHMTHF). The highest yields (88-91%) to DHMTHF are achieved using Ru supported on materials with high isoelectric points, such as ceria, magnesia-zirconia, and γ-alumina. Supported catalysts containing Pt and Pd at the same weight percent as Ru are not as active for the selective hydrogenation to DHMTHF.
Article titled “Hydrogenolysis of glycerol to 1,2-propanediol over Ru—Cu bimetals supported on different supports” by H Liu et al. published in CLEAN—Soil, Air, Water, March 2012, Volume 40 (3), pages 318-324 reports a series of Ru—Cu bimetallic catalysts were prepared using different supports in an attempt to develop highly efficient catalysts. Hydrogenolysis of aqueous solution of glycerol was performed with the supported Ru—Cu catalysts. The bimetallic catalysts were very efficient for catalyzing the hydrogenolysis of glycerol compared with the corresponding monometallic catalysts. One hundred percent of glycerol conversion and 78.5% of 1,2-propanediol yield could be achieved at 180° C. and 8 MPa.
Article titled ‘Production of dimethylfuran from hydroxymethylfurfural through catalytic transfer hydrogenation with ruthenium supported on carbon” by J Jae et al. published in Chem Sus Chem, July 2013, Volume 6, Issue 7, pages 1158-1162 reports transfer hydrogenation using alcohols as hydrogen donors and 5 wt % Ru/C catalyst results in the selective conversion of hydroxymethylfurfural to dimethylfuran (>80% yield). During transfer hydrogenation, the hydrogen produced from alcohols is utilized in the hydrogenation of hydroxymethylfurfural. The first step is dehydration of fructose to give 5-hydroxymethyl furfural (HMF); in the second step, using copper chromite (CuCrO4) or CuRu/C catalyst HMF hydrogenolysis reaction is carried out, to give DMF; yield of DMF was 79%.
Article titled “Ruthenium nanoparticles supported on zeolite Y as an efficient catalyst for selective hydrogenation of xylose to xylitol” by D K Mishra et al. Published in Journal of Molecular Catalysis A: Chemical, Volume 376, September 2013, Pages 63-70 reports Zeolite Y (HYZ) supported ruthenium (Ru) nanoparticles catalysts prepared by simple impregnation method and characterized by using different techniques such as TEM, TEM-EDX, SEM, XRD, FT-IR, surface area analysis and CO chemisorption. The reaction conditions are optimized by varying the stirring rate, ruthenium percent loading, xylose concentration, hydrogen partial pressure, reaction temperature and amount of catalyst to achieve the maximum conversion of xylose and selectivity to hydrogenated product xylitol.
Article titled “Efficient production of the liquid fuel 2,5-dimethylfuran from 5-hydroxymethylfurfural over Ru/Co3O4 catalyst” by Y Zu et al. published in Applied Catalysis B: Environmental, Volume 146, March 2014, Pages 244-248, available online from Apr. 24, 2013 reports Ru/Co3O4 catalyst prepared by a simple co-precipitation method used to catalyze the conversion of 5-hydroxymethylfurfural (HMF) into 2,5-dimethylfuran (DMF) for the first time and exhibited excellent catalytic performance and 93.4% yield of DMF achieved at relatively low reaction temperature and H2 pressure (130° C., 0.7 MPa). Higher loading of Ru (5 wt %) was used to prepare this Ru/Co3O4 catalyst. Moreover, longer reaction time (24 h) is needed to achieve good yield of DMF (93.4%).
Most of reported processes do not offer good space time DMF yields and are having many other drawbacks such the high metal content of the catalyst, the catalyst is not recyclable and need high H2 pressure. Few processes have been reported with formic acid or 2-propanol as reducing agents, but these are either economically not feasible or commercially difficult to practice.
Therefore, there is need in the art to develop an environment friendly process for the preparation of DMF from HMF which can overcome prior art problems in terms of space time yield, recyclability, H2 pressure and time.